Elecric-current controller.



PATENTED MAY 29, L905.

Roi 821,697.

w, L. BRADLEY.

ELECTRIC CURRENT CONTROLLER.

APPLICATION FILED JUNE 9. 1904.

6 SHEETS-$113111 1.

PATENTED MAY 29, 1906.

L.BRADLEY. ELECTRIC CURRENT CONTROLLER.

APPLICATION FILED JUNE 9. 1904.

5 SHEETS-SHEET z.

J J h 'PATENTED MAY 29, 1906.

L. BRADLEY. ELECTRIC CURRENT GONTROLLE APPLIOATIION FILED JUNE 9. 1904.

6 SHEETS-SHEET 3.

'No. 821,697 PATENTED MAY 29, 1906.

' LBRADLEY.

ELECTRIC GURRBNT CONTROLLER.

APPLIUATION FILED JUNE 9. 1904.

N0, 21,697. PATENTED'MAY 29, 1906. I

L. BRADLEY.

ELECTRIC CURRENT CONTROLLER.

APPLICATION FILED JUNE 9, 1904.

(iv-SHEETS-SHEET 5.

J8 hwma $51): $10M W 2 Unrrnn srarns LYNDE BRADLEY, OF MILWAUKEE,

PATiilhlT ifiili iii i l ELECTRiC-CURRENT CONTROLLER.

Specification of Letters Patent.

Patented May'29, 1906.

Application tiled June 9,1994:- sfiiial NO- 211,7 i2- To all whom it may concern:

Be it known that l, LYNDE BRADLEY, a citizen of the United States, residing at Milwaukee, in the countyofMilwaukee and State 5 of Wisconsin, have invented certain new and useful Improvements in Electric-Current Co 11- trollers, of which the following is a specification, reference being had to the accompanying drawings, forming a part thereof.

This invention relates to controllers of the class for which United States Letters Patent No. 723,817 were issued to me March 31,

- 1903, and in which a compressible resistance medium is subjected to a variable pressure to gradually change its electrical conductivity and regulate the flow of current.

The main objects oi the present invention are to equalize and reduce the manual eilort required to operate the controller by increasing the power of the compressing mechanism as the reaction of the resistance inc- 7 diuni is augmented by increased compression, to restore and maintain the normal re sistance or low conductivity of the resistance medium when it is relieved from pressure, to

. eii'ectively avoid orstop arcing and prevent injury to the switch contact-pieces and other parts of the controller when the circuit is broken, to provide for the quick and easy removal and renewal oi the resistance units and other'parts of the controller, and generally to improve the construction and operation of controllers of this class.

It consists in certain novel features of con- 5 struction and in the peculiar arrangement and. combinations of parts, as hereinafter particularly described, and defined in the claims.

In the accompanying drawings like characters designate the same parts in the several figures.

Figure 1 is a generally vertical section in a brokenor irregular plane indicated by the line 1 1, Fig. 3, and an elevation showing particularly the construction and arrai'igcmcnt of the resistance units, and oi the compress ing mechanism in a controller embodying my invention. Fig. 2 is an elevation. of the reverse side of' the controller, snowing particularly the switching incchani. n constituting a part of the controller. l 1g. 3 is a vertical section of the controller in a plane indicated by the lines 3 3, Figs. 1 and 2. Figs. 1, 5,

6 (5, respectively, on Figs. 1, 2,

and 6 are horizontal sections of the controller in planes indicated by the lines 4 4, 5 5, and and 3; and 1 Fig 7 is a diagram illustrating the circuit connections of the controller.

The operation of the controller to which ,my present improvements relate depends upon the fact that the resistance of divided or disintegrated electrical conducting substances varies according to the pressure to which they are subjected. This is true in a very marked degree with carbon, and for this reason this material is preferably employed as the resistance medium in my improved controller.

For the purpose of illustrating and explainent invention 1 have shown and will particularly describe a series reversible controller, although the invention is applicable to other types of controllers by such changes in the arrangement of partsand in the electrical connections as will be obvious to persons skilled in the art to which the invention pertains.

The carbon which serves as the resistance medium is formed into plates or disks which are arranged, as shown in Fig. 1, in piles or columns a. Each pile or column is inclosed. and insulated by a tube 1), preferably formed of loosely-wrapped asbestos-paper without glue, paste, or other binder. This has, been found to be the most effective, durable, and satisfactory insulation for the carbon columns. For protection and sup ort the colin metal tubes or cases 0, which are threaded rated ca s (1. At their upper ends they are provider with perforated caps e, which are clamped with insulating-bushings in place, as shown in Figs. 1 and 3.

Each carbon column terminates at the ends with copper-plated carbon blocks,which are thicker than the intermediate disks and bear against metal studs or lugs f and g. The studs f pass through ant? are insulated from the caps d at the lower ends of the tubes, and they are electrically connected in pairs or otherwise by metal plates orconductors, as shown in Fig. 1.

The studs or plugs g, which for the sake of lightness are preferably made of aluminium,

in the im rovemcnts constitutin n1 res c l P at-their lower ends and provided with perfouinns thus covered and insulate are inclosed 'rarriage.

so as to exert normally lnfie pressure on the carbon columns, are secured by SCI/W5 or oth erwise to the upper copper-plated blocks, as shown in Fig. 1, thus forming carbon-tipped electrodes and insuring good electrical contacts and connect-ions at the upper ends of the carbon columns, and they pass loosely through and are movable up and down in the caps c, with which they are connected by flexible conductors, saidcaps being also connected by flexible metallic bands 72. or other suitable conductors with bin ing-posts on the back of the slate panel or su'itclvbase i. The carbon piles or columns constitute the resistance units of the controller.

Air being excluded from the tubes 0, e:-: ceptwhat .may enter through the small openings at their upper ends in the caps 6 around the plugs g, disintegration and consumption of the carbon, even if heated to a high temperature, are prevented. Whatever air may remain in or enter the tubes is expelled and displaced by carbon-dioxid gas, which is produced by heat developed in the operation of" the controller and which, as is well known, prevents oxidation or combustion.

The caps (Z, formed with reduced extensions at their lower ends, are loosely fitted in openings in a plate which is mounted upon and insulated from a carriage or verticallyniovable support 7r. This carriage is [astened to a vertical rod Z, which is guided at its upper and lower ends by hearings in the frame of the controller, the upper hearing being attached to and insulated from the tuberack m and the lower hearing being formed in the bottom. girder or cross-piece it of the frame. The tube-rack .12., in which the upper ends of the tubes 0 are guided and held in place by removable rods 0, is attacl'ied' at its ends to and insulated from the sides p of the frame. By simply withdrawing the rods 0 and detaching the electrical connections at the upper ends of the tubes said'tubes can be readily removed from the controller and replaced.

The extensions on the caps (Z, which enter the openings in the plate j, are formed, as shown in Figs. 1, 3, and 6, withlugs, and the openingsin said plate are formed on one side with .cawresp'onding notches to receive said lugsand insure the tubes 0, with the electrical connections at their upper ends, being placed andheld in the controller in their 'prol'ier positions. Openings in the. carriage r to receive the extensions on lhe lower ends of the plug (1, are made somewhat larger than the corresponding openings in the plate j, so as to in sure the insulation of the tubes c from the Above the lubes'e the ermiroller provided with a yielding equalizer by which the pressure exerted mien the several. resistance units equally distributed between them, ij crushing of the carbon. is prevented, varia- 1 tion in the length of the columns a, due to eX- pansion and contraction under varying temperaturcs, is allowed, and a sullicient range of movement of the operating-lever is per mitted for practical operation of the controller. This equalizer comprises rockers q q, centrally pivoted to the ends of a rocker 1', which is in turn centrally pivoted to a cross bar 8. ends on rods t t, which are guided in hearings on the sides p p of the frame in lines parallel with the guide-rod L of the carriage it. The equalizer is yieldingly held in its normal position toward the carria e by springs u bearing at their lower ends against nuts and interposed washers on the rods and at their upper ends against lu s on the frame. The rockers q q are provi ed above and in line with the studs or plugs g with insulated abutments or bearings 11'. The downward movement of the equalizer is limited by the en- The bar 8 is adjustably secured at its gagement of shoulders on the rods t with the lower guiding-lugs on the frame.

The guiderods t t are threaded in the bar 8, which is secured therein by jam-nuts, and the upper ends of said rods are slotted and accessible through holes in the top of the controller-frame for the purpose of turning them with a screw-driver and adjustingthe equalizer toward and from the resistance units. The tension of the springs u a is readily a'djusted by turning the nuts at their lower ends up or down on said rods.

The operating-lever w is fulcrumed at its lower end to the girder or cross-piece n of the frame and is provided on opposite sides of its axis near its fulcrum with rollers as :0, upon which the carriage k normally bears, as seen in Figs. 1 and 2. At its upper end this lever is provided with. a suitable handle and also with aroller g, which is movably mounted. thereon and yieldingly held by a spring 2 against a curved track or runway 3 on the top or upper part of the frame. This runway is formed with a central depression in which the roller y rests when the operating-lever is in its initial and neutral position, as shown in Figs. 1 and 2. For a short distance on each side of this depressimi the runway is lorn'ied to a curve approximately concentric with the fulcrum of said lever, and then it gradually approaches said fulcrum toward its ends, the radius of the curve becoming shorter.

ln co'i'mection with the variable resistance and com ')rcssing and equalizing devices of the (amtroller, the following switch mechanism for turning the current on and oil from the resistance, n'og essivel y short-circuiting the resistance in sections when the full current is onfalid reversing the current is provided. .Upon the plate panel or other suit.-

.able insulating-bas 4 are mounted in pairs eontact plates 4-, 5, G, 7, 8, 9, and ll), thetwo platesol' each' pair being arranged on apnosite sides of the central or neutral position ol the operating-lever. Upon the operatinglever are mounted two insulated brush-holders 11, each of which is provided with two pairs of carbon or other brushes or contactpieces 12, movably held therein and yieldingly pressed toward the fiXedcontact-plates on the bns'v i by'sprin'gs 13, acting upon and "through yokes 14-, one set of brushes being arranged .to span and electrically connect the re contact-plates 4, 8, or 9 with the plates 5 and l the other set to connect the contact-plates 6 with the plates 7 or on either side of the center, according to the direction in which I .the operating-lever is turned. The contactplates 5 and Gare for the purpose of reversing the current, the contact-plates 9 and 10 are for progressively short-circuiting or cutting out the resistance medium In sections when the full current is on, and the contact-plates 2o 8 are made separate and insulated from the contact-plates 4 for the purpose of renewal and for connecting ablow-out magnet in series with the plates 4 and 8, so that said magnet will be included in the circuit onlywith 2 5 the full resistance or when the least current is flowing through the controller. Between the.

two sets of contactlates on each side of the controller the pane i or switch-base is provided withfiber or other insulating plates 15 of the same thickness on which the brushes 1.2 bear when the operating-lever is in its central position. The blow-out magnet 16 has a forked pole-piece 17 projecting through openings in the slate panel i adjacent to the 5 inner edges of the contactlates 8 to concen- I each other at one end in pairs.

trate the magnetic lines 0' force at the most effective points for extinguishing arcs when the circuit is broken.

Referring to Fig. 7, illustratingthe electrical Iconnections for a series reversible controller like that herein shown and described, the resistance units a c are connected with One of the pints is connected at the other end with the utnct-plates 4,-while theother unit of the,

same pair ,is connected with the contact-, plates 9. One unit of the other pair is connected with the contact-plates 7, While the other unit of this pair is connected with the .50. contactlates 10 and-with one main or supply con u'ctor 18. The plates 9 are connect ed with the other main or supply conductor The plates 5 and 6 are .cross oonnected, and the. ,p plates 6 are connected by conductors 21 with.

19 through the field 20 of the motor.

thejarmatureQZ of the motor. The coil of the blow-out magnet 15 is connected with each of the; plates 4 and 8 around or across the spaces between them. Of course it will beunderstood that the arranglement of the parts of the controller and t eir electrical connections may. be varied to adapt the controller to motors of different types and for different kinds of work.

My improved controller herein shown and described operates as follows: Assuming that the mam or supply conductors 18 and 19 are connected with a source of electricity and that the controlling-lever is in its middle and neutral position, as shown in Figs. 1 and 2, no current will flow through the motor or controller. turned in either direction from its central position sufficiently to carry the brushes 12 into engagement with the contactplatcs for example, if it is turned to the left, as shown in Fig. Lethe roller 'y will be carried out of the central depression in the track 3 upon a raised portion thereof, thereby further compressing the spring 2, and-the circuit will be closed through the controller, current flowing from the line 19 through the field 20 of the motor, as shown in Fig. 7, thence thro h the left contact-plate 9, onepair of the resistance units 0, the blow-out magnet 15, the leftcontactlate 8, the left upper pair of brushes 12. t e left contact-plate 5, the right contact-plate 6, thence through the armature 22 of the motor back to the left contact-plate 6, through the lower left pair of brushes to the left contact-plate 7, thence through the other pair of resistance units 0 to the line 18. The continued movement of the lever in the same direction will operate, through the roller ."c at the right, as seen in Fig. 2, to lift the carriage 7c with the resistance units until the plugs g at their upper ends are brought into engagement with the bearing-pieces 'U of the equalizer. The re sistance medium, consisting of the columns a. 'of carbon disks, will then be gradually compressed, the pressure being equally distributed by the rockers q and rbetween the several resistance units. As the lever is moved farther to the left the springs u will be compressed, the cross-bar s with the rockers will yield upwardly, and the pressure on the carbon columns will be gradually increased, thereby reducing their resistance to the flow of current. As the pressure upon the carbon is increased and its resistance reduced it reacts with augmented force upon the operating-lever, tending to carry it backto its initial position; but the power stored in the compressed spring 2, acting through the roller .y upon the track or runway 3, tends to turn the lever away from its central position with a gradually-increasing, force, according to the itch or inclination of the runway'3, which is ,so designed that the force exerted by the s ring 2 through said roller y, tending to turn the lever in one direction, will approximately equalize the reaction of the compressed rein the opposite direction. The power required to operate the controller is thus distributed over the entire traverse of the operating-lever, and the compression of the resistance medium is effected with the expenditure of much less effort or energy than would If now the operating-lcvcr w is sistance medium, tending to move the lever IIO otherwise be required. As the operatinglever a preaches the outer'limit of its move- -'n 1ent' t e lowerbrusir 12 passes-oil from the contact-plate 7 upon the contact-plate 10, thus cutting out or short-circuiting the resistance units 0 connected with the plate 10. The upper brush thereupon passes from the contact-plate 4 upon the plate 9', cutting out or short-circuiting the rest of the resistance units after they have been compressed to the fullestextent and their'resistance to the current reduced: to a minimum. hen the lever is inits final or extreme position with the brushes resting on the contact-plates 9 and 10, the current will flow from the main 19 through the motor-field 20 thence through contact-plate 9, brushes 12-, contact-plates 5 and 6, armature 22, contact-plate 6, brushes 12, contact-plate 10, to line 18 without passing through any of the resistance units 0. As the lever is moved back to its middle position and the upper brushes pass over the contact-plate 8 the circuit is closed through the blow-out magnet 15-, when the resistance units, relieved of ressure, have again assumed theirnorma condition of high resistance. As the last brush passes oil from the contact-plate 8' any are that may be formed will be instantly extinguished by said magnet. .The blow-out magnet, connected as herein shown and described, carries only the starting or minimum current, and therefore may be woundto work with much greater efhciency than" it it was made to carry the full-load current, since it isrequired to extin uish arcs only when the circuit is broken wit the full resistance included therein. The contact-plates 8' at which the' circuit is broken being most liable to injury from areing or sparking are made separate from the lates 4, sothat they may be easily renewed, besides affordingrneans of cutting the blowout magnet 15 out of circuit except when the full resistance is included therein. During the return movement of the operating-lever to its middle position the spring .2 is reconn pressed as the roller passes over the higher portion of the track or runway 3, and power is thus stored to compress or aid in compressing the resistance medium, when the circuit is again closed through the controller and the lever w is moved a sulficient distance in either direction from its middle or neutral position, as above explained. \Vhen the roller passes over' the crest on either side of the central depression. in the track upon either of the sloping sides of saidd'eprcs slon, the spring 2 reacts to bring the lever w instantly to its central position, thus making a simple and effective quick-break switch. This automatic centering function of the spring-actuated roller 1 also operates to bring the carriage k and the upwardly-mm mg roller :c on the operating-lever together with sufiicient force to par the resistance units and restore them to their normal condition of high resistance. This feature of the device is of great advantage, since the carbon columns are apt to become compacted with continued use of the controller and will not then of themselves regain their original condition of high resistance when they are relieved from pressure. It will be observed that when the operating-ha m? is turned in either direction from its middle position and approaches the outer limits of its movement the leverage of the rollers a: on the carriage l". increases as pressure upon and reaction of the resistance medium is augmented. Thus the arrangement of these rollerscooperates with the spring-actuated roller 1 and the curved track 3 to overcome the reaction of the resistance medium when bjected to pressure. By turning the opera ting-lever to the right, as seen in Fig. 2, the current will be reversed through the armature of the motor,

and the resistance will be gradually reduced and finally cut out of the circuit in the manner hereinbe'iore explained.

The number of the resistance units may be varied, and they may be variously grouped and: connected according to the requirements of varying conditions, so as to cut out or short-circuit more or less of them at a time by means of the separate switch-contact pieces 9 and 10 as, for example, with the four units shown in. the drawings, three instead of two may be connected with. the contact-pieces 10 and only one with the contactpieces They are, however, preierabhxarranged, as shown, in a single row, so as not to increase the depth of the controller in a direction perpendicular to the plane in which the operating-lever moves.

V arious changes in the details ofconstruction and arrangement of parts and electrical connections may be made without departing; from the principle and intended scope of the invention.

I claim 1. In an electric-current controller the combination of a resistance medium and mechanically-operated means adapted to subject said medium to pressure and to act witl augmented power as the pressure upon said medium is increased, substantially de scribed. 4

" 2. In an electric-current controller the combination of a resistance medium whose electrical conductivity increased when it is subjected to pressur and. manually-operated means adapted to exert an increasing pressure upon said medium. with a substantially constant expenditure of energy, substantially as described, I I V 3. In. an electric-current controller the combination or" a compressible resistance medium whose conductivity is increased by pressure, and mechanically-operated m ans adapted to exert a gradually-increasing p essure upon said medium as'its reaction under augmented pressure mcreases, without the application of correspondinglyincreasing ener substantially as described.

1 4. In an electric-current controller the combination of a resistance medium whose Isure, amanuallysoperated lever ada ted to exert pressure upon said medium, an means A forlincreasing the power exerted by said lever as thereaction ot'said medium is augmented x'by increased compression, substantially, as described.

' 5. In an electric-current controller the combination of a resistance medium'whose electrical conductivity is varied by pressure, means for compressing said medium and means for storing the power exerted by the reaction of said medium upon. said compresshing" means and lo'r app ying such stored power to the operation of said compressing means;substantially as described. p6 In' an el'cctriccurrent controller the combination of a compressible resistance medium whose electrical conductivity is inq crcased by pressure, a lever arranged to compress said medium and means for storing the power exerted by the reaction of said mediumiipon said lever when moved in one di rcction and for applying such stored power to the operation oi said lever when moved in the other direction to co n'ipress said medium;

substantiallyas described. a v ,7. In an electr current controller the i'combinationof a co ipressible resistance medium, means for subjecting said medium to a variable pressure to grai'lually change its ,lectrical conductivity and means tending to 1' applied to operate the "lll't degrees ol' compres sion, substantially as described.

In. an electric current controller the combination ot a resistance medium, a lever i arranged to gradually compress said medium Y and provided with a roller :movably mounted thereon, a track or runway forsaid roller and means holding saidroller with yielding ressure against saidtrack or runway, whic has 'avar'ying r a; vaturc or inclination constructfed and arranged to hold said lever at rest in i f any position inahieh may be left, substantiall y as described (Lin an electric currcn't controller the v I con'ibii'urtion oi a resistance medium, a lever arrang d to gradually compress said medium and provided with a roller movably mounted the eon, anriunviiy gradually approaching the ljuicrum oi ll'l'iQYU-l". toward the end op positetne i1 rial or'nr-utral position of thelev.1, and means tending to forcesaid roller v against said rimwa substantially described. U I id. In an electric--current cont-roller the combiuamin of a compressible resistance me- 1 electrical conductivity is increased by pres di-um whose electrical conductivity is varied 6 5 by pressure, a, lever arranged to gradually compress said medium and provided with a roller movably mounted thereon, a track or runway for said roller having a depression,

and means yieldingly pressing said roller against said track and adapted'to automatically complete the return movement of said lever to its neutral position, substantially as I described.

"ll. In an electric -current controller the comblnatlon of a compresslble resistance medrum whose electrical conductivity is varied by pressure, a lever arranged to gradually compress said medium and provided with a roller movably mounted thereon, a track or 8o runway having a depression, switch-contact pieces, one of which is carried by said lever,

and .means yieldingly ressing said roller a ainst said track and a apted toautomatica y complete the return of said lever to its 5 neutral position and to quickly break the circuit, substantially as described.

12. In an electric-current controller the combination of a resistance medium, a lever arranged to gradually compress said medium and provide with a roller movably mounted thereon, a runway having a depression and gradually approaching the fulcrum of said lever as it recedes from said depression, and means holdin said roller against said runway and ten ing to move the-lever away from said depression with gradually-increasing power, and to quickly complete its return movement tothe neutral position when I said roller iscarried to one side of said depres- 10o sion, substantially as described.

13. In an electric-current controller the combination of a carriage, a compressible resistance medium mounted upon and movable withsaid carriage, an abutment against which l 0 5 said medium is arranged to be compressed, a lever adapted to move said carriage toward said abutment and provided with a roller movably mounted thereon, a track havin'ga depression, and means yioldingly holding said roller against said track and adapted to j quickly complete its return movement when the roller reaches said depression and tojar said resistance medium as the carriage is brought to a stop, substantially as described. I I 5 14. In an electric-current controller the combination of a resistance medium whose electrical conductivity is varied byprcssure, meansfor'excrting a variable pressure upon said resistance medium, and means for re- I20 storing and maintaining the normal resistance of said medium, substantiallyas deseribed.

1.3. In an electric-current controller the ,C-OIIllJillfilllOD of a resistance medium whose i 25 electrical conductivity is increased by pressure, mcans i'or.subjectingsaid medium to a variable pressure, and means lor arring said medium whereby it is restored to its original state of high resistance, substantially as described.

16. In an electric-current controller the combination of a movable resistance medium whose electrical conductivity is increased by pressure,an abutment or bearing, and means for subjecting said medium to av variable pressure by moving it with more or less force against said abutment and for jarring said medium and restoring its normal resistance in moving it back to its initial position, substantially as described.

17. In an electric-current controller the combination of suitable frame, provided with an abutment, a movable support, a case mounted upon said support and movable therev ith toward said abutment, a compressible resistance medium inclosed in said case and means for moving said support with said.

moving said carriage to and pressing said resistance units with more or less force against said equalizer, substantially as described.

19. In an electric-current controller the combination of a carriage or movable support, a number of resistance units mounted upon and movable with said carriage, a yieldi mg equalizer and an operating-1ever arranged to move said carriage and resistance units with more orless force against said equalizer and to subject said resistance units to an equally-distributed variable pressure, substantially as described.

20. In an electric-current controller the combination of a yielding equalizer, a carriage movable toward and from said equalizer, a number of resistance. units whose electrical conductivity is increased by pressure, mounted upon said carriage, a lever adapted to move said resistance units with said carria' c againstsaid equalizer, and provided witi a roller movably mounted thereon, a runway for said roller gradually approaching the fulcrum of said lever as it recedes from its neutral position, and means tending to force said roller against said runway, substantially as described.

21. I11 an electric-current controller tlu combination with a suitable frame, of a resistance medium whose electrical conductivity is varied by pressure, removably mounted in said frame and having detachable electrical connections and means for subjecting said medium to pressure, substantially as described.

22. In an electric controller the combination with a suitable frame, of a compressible resistance removably mounted in said frame, means insuring its being placed andheld in the proper position in said frame, and means for subjecting said resistance to pressure, substantially as described.

23. Inan electric-current controller the combination with a suitable frame, of a number of tubes loosely held at one end in said frame and containing a resistance medium whose electrical conductivity is increased by pressure, a rack on said frame provided with one or more removable rods for holding said tubes in place therein, and means for subjecting the resistance medium to a variable pres sure, substantially as described.

24. In an electric-current controller the combination of a variable resistance, means "for closing and opening the circuit through said resistance, a blow-out magnet arranged to extinguish arcs formed by breaking the circuit through said resistance, and means for cutting out said magnet before all the resistance has been out out of the circuit and for bringing said magnet into the circuit berore it is broken and while it includes such resistance, substantially as described.

25. In an electric-current controller the combination of a variable resistance, means for closing and opening the circuit thror g'h said resistance comprising movable and insulated contact-pieces, and a blow-out magnet connected across the space between the insu lated contact-pieces over which the movable contact-piece passes only when high resistance is included in the circuit, substantially as described.

26. In an electric-current controller, the combination of a resistance medium whose electrical conductivity is varied by pressure, a stationary switch-base provided with insulated contact-plates connected and arranged to reverse the current and to open and close the circuit through said resistance medium, and an operating-lever provided with brushes or contact-pieces and adapted to be moved in l pposite directions from a normal or neutral position and When moved from such position in either direction to first close the circuit illlnr.! .','l1 said resistance medium and then subject the same to a gradually-increasing pressure, substantially as described.

27. In an electric-current controller the combination of a number of resistance units whose electrical conductivity is varied by pressure, means for subjecting said resistance units to a variable pressure, and switching devices arranged to cut out or shortcircuit said resistance units in groups or sections one alter another when they are subjected to high compression and ofi'er little or no resistance to the current, substantially as described.

28. In an electric-current controller the combination of a carriage, resistance mounted thereon and composed of material whose abutment against which said resistance is pressed'by the movement of said carriage, and an operating-lever provided in a line transverse to its axiswith two rollers each or which is arranged to approach a perpendicular passing through the fulcrum oi the lever to the carriage when sa'idlever is moved in one direction away from its neutral position and to move said carriage toward said abutment with gradually-increasing power, substantially as described.

30. In an electric-current controller, a resistance unit composed 01 a column of current-conducting disks, having a cover of non-combustible insulating material loosely wrapped around it and inclosed in a protecting and supporting tube, substantially as described.

ii'lf-ln an; ,eleetric current controllers/the combination of a compressible resistance medium, and a yielding equalizer against which said resistance is compressed, con'iprising a bar, screw-threaded guide-rods on which said bar is adjustably secured and adjustable springs tending to press said bar toward said resistance medium, substantially as de scribed.

32. In an electric-current controller the combination ol a compressible resistance medium and a carbon-tipped metallic electrode, adapted to'bear against and formal] electrical contact with said resistance medium, substantially as described.

33. In an electric-current controller the combination of a compressible resistance medium whose electrical conductivity is increased by com ression and a lever adapted to compress sai medium and to act thereon with greater power as the compression and reaction of said medium are increased, substantially as described.

In witness whereof I hereto aflix my signature in presence of two witnesses.

LYNDE BRADLEY Witnesses CHAS. L. Goes, BERNARD O. Rororr. 

